| 摘要 |
831,503. Waveguides. GENERAL ELECTRIC CO. Ltd. Oct. 25, 1957 [Oct. 26, 1956], No. 32809/56. Class 40 (8). In order to prevent radiation from a longitudinal or helical slot 2, Fig. 1, in a waveguide 1, an external member 4 is arranged adjacent the slot in such a manner that it forms with the waveguide wall 3 a transmission line supporting an evanescent mode of propagation. It is stated that the transmission line is excited in such a mode if where N1, N2 are respectively the refractive indices of the dielectric filling of the waveguide and the transmission line and #o, #c are respectively the free-space and cut-off wavelengths of the energy propagated in the H11 mode in the waveguide. The slot may be provided to prevent the waveguide wall from forming a shortcircuited turn when it is surrounded by a solenoid, as, e.g., in a Faraday-element gyrator. In an apparatus of this type (Fig. 2) the waveguide may comprise a tube 16 of polystyrene which is formed with an external conductive layer 15 by a chemical silvering process followed by electroplating. A longitudinal slot 20 and two terminal circumferential slots 22 (one only shown) are formed by sticking filaments on the tube 16 during the silvering process and stripping them off before electroplating. The longitudinal slot is co-terminous with an axial ferrite element comprising a number of cylindrical portions 14a and two tapered end-portions 14b arranged within the bore of the polystyrene tube 16. The ends of the tube are plugged with shaped polystyrene members 17. The longitudinal slot is covered by a conductive arcuate plate 24 spaced from the waveguide wall 15 by loops, strips or a helical winding 25 of, e.g., polyethylene. The plate 24 is held in position by a winding of tapes 26 and a solenoid 27 is wound over the tapes between cheeks 28. Coupling flanges 29 are electrically connected to the waveguide wall 15. Where the energy propagated in the waveguide is circularly polarized, operation over a broader band may be obtained by the use of a helical slot of rotary sense opposite to that of the wave. Four slots symmetrically arranged around the circumference of the guide may be used. |
